Better fix for gcc optimization issue

According to the standard, compiler is free to choose
the enum type as long as can keep its data.
Also cast to short and right shift are implementation
defined in case of a signed integer.

Normally all the compilers implement this stuff in
the "usual" way, but gcc with -O3 and -O2 pushes
aggressively the language to its limits to squeeze
even the last bit of speed. And this broke our
not 100% standard conforming code.

The fix is to rewrite the Score enum and the 16 bits
word extracting functions in a way that is 100% standard
compliant and with no speed regression on gcc and also on
the other compilers.

Verified it works on all compilers and with equivalent
functionality.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

diff --git a/src/Makefile b/src/Makefile
index d5a72b66f5a5a829c98ca7270687e26a1a906c06..1388f465fd49a0c00e1a52c3bec993aebfafe8b1 100644 (file)
--- a/src/Makefile
+++ b/src/Makefile
@@ -25,11 +25,8 @@ EXE = stockfish
 ### ==========================================================================
 ### Compiler speed switches for both GCC and ICC. These settings are generally
 ### fast on a broad range of systems, but may be changed experimentally
 ### ==========================================================================
 ### Compiler speed switches for both GCC and ICC. These settings are generally
 ### fast on a broad range of systems, but may be changed experimentally

-###
-### NOTE: Some versions of gcc miscompile value.h with -O2 or -O3, this is the
-### safe setup, try changing to -O3 or -O2 and verify it works for you.

 ### ==========================================================================
 ### ==========================================================================

-GCCFLAGS = -O1 -msse
+GCCFLAGS = -O3 -msse

 ICCFLAGS = -fast -msse
 ICCFLAGS-OSX = -fast -mdynamic-no-pic
 
 ICCFLAGS = -fast -msse
 ICCFLAGS-OSX = -fast -mdynamic-no-pic
 

diff --git a/src/value.h b/src/value.h
index fec6516a4c8c4014427afeeb3cf22d6b9941d865..364844555abead4ca5b79d62a819f024c6cad5a8 100644 (file)
--- a/src/value.h
+++ b/src/value.h
@@ -56,10 +56,22 @@ enum Value {
 /// integer (enum), first LSB 16 bits are used to store endgame
 /// value, while upper bits are used for midgame value.
 
 /// integer (enum), first LSB 16 bits are used to store endgame
 /// value, while upper bits are used for midgame value.
 

-enum Score { ENSURE_32_BIT_SIZE = 1 << 31 };
-
+// Compiler is free to choose the enum type as long as can keep
+// its data, so ensure Score to be an integer type.
+enum Score { ENSURE_32_BITS_SIZE_P = (1 << 16), ENSURE_32_BITS_SIZE_N = -(1 << 16)};
+
+// Extracting the _signed_ lower and upper 16 bits it not so trivial
+// because according to the standard a simple cast to short is
+// implementation defined and so is a right shift of a signed integer.
+inline Value mg_value(Score s) { return Value(((int(s) + 32768) & ~0xffff) / 0x10000); }
+
+// Unfortunatly on Intel 64 bit we have a small speed regression, so use a faster code in
+// this case, although not 100% standard compliant it seems to work for Intel and MSVC.
+#if defined(IS_64BIT) && (!defined(__GNUC__) || defined(__INTEL_COMPILER))

 inline Value eg_value(Score s) { return Value(int16_t(s & 0xffff)); }
 inline Value eg_value(Score s) { return Value(int16_t(s & 0xffff)); }

-inline Value mg_value(Score s) { return Value((int(s) + 32768) >> 16); }
+#else
+inline Value eg_value(Score s) { return Value((int)(unsigned(s) & 0x7fffu) - (int)(unsigned(s) & 0x8000u)); }
+#endif

 
 inline Score make_score(int mg, int eg) { return Score((mg << 16) + eg); }
 
 
 inline Score make_score(int mg, int eg) { return Score((mg << 16) + eg); }